Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
07~7
EST~IQD ANI:) APPARATU~ RAl!E P~CIJ3~h~INEI)
WALL B~ ,INt3 ~'rR~J3
BAC~GROUN~ OF THE INVENTION
1. Field of the Invention
The i~vention relates to methods and apparatus for causing
the mi~ing o~ ubstances and fluids at interfaces with Yarying
density ~radi~nts. ~ore parti~ularly-the invention describes a
method of gen~rating precisely-defined wall she~ring stresses at
a substrate/fluid interface, especially those of a sediment/~ater
inter~ace within a confinod space, to~ther with an apparatuq to
reali~e this method.
2. Description of the Prior Art
- Wall shearinq ~tresses play a pivot~l role in
hydrodynamical, sedimentologi~al, biological, geochemical, and
engineering processes and their control at substrate/fluid
iater~aces. The inv~stigatio~ of sediment/water boundary layers
i~ rivers, lakes, and o~eans i~ of great importanc~; ~.9., the
determination of the vertical e~change ~flux) of chemic~l
substances betwee~ ~ediment and overlyiny wat~r, or the
determination of porewater concentration profiles as ~ell as the
r~serYoir capacity of sediments for chemical sub~tance~ in~ludin~
adsorb0d pollut~rlt~. The latter ~:oncerns waste disposal, pathways
o~ toxirl and ~nvironmental health. In ord~r to achieve
3-2~07~:~
realistic results in these areas, it is mandatory to establish
quantitatively the link between the studiPd process and the wall
shearing stres~es at the substrate/fluid interface. To achieve
thi~ ~oal a flow pattern in the ~luid has to be generated which
produces precisely known wal 1 shearing stresses in the
~ubstrate/fluid boundary layer.
The generation of a boundary layer structure homogeneous
over a relatively large surface area betwee~ a substrate and
overlyins fluid with a resulting spatially homogeneous
distribution o:E the wal 1 shearing stress over the whol e area can
be relevant also for industrial prc~cessing and manufacturing
techniques, especially in microbiological manufacturing
te~hniques, titration processes, sur~ace ~oatings, and others.
It is also useful in establlshing the best possibl~ growth
enviro~ment for bacterial cultures or to optimize their exudates.-
The invention has thus the task to find an engineeringprocedure a~ well as an apparatus which permits the generation of
precisely defined wall shearing stress fields in a
substrate/fluid bou~dary layer ~ithin a confined measuring volume
for steady and variable time histories.
"Precisely defined" wall shearing stresses means that their
mag~itude generated at any point and time on the surface of the
s-~bstrate in th~ ~onfined measuriny volume is known within a
measurin~ uncertainty (mean error) of less th~n 10~. Depending
o~ desired application, these distributio~s ~an have different
~ ~ ~ O 7 4.~
spatial and temporal features as hereafter sho~n.
SUMMAR~ OF THE INVENTION
The invention provides an engineerin~ method and apparatus
for generating an a~ial-symmetric rotation of ~luid while
simultaneously remoYing a defined fluid volume in the center of
a rotational a~is and causing it to be recirculated or collected
with sllbstitut~d fl~lid volume returned to the me~suring volume
instead.
The apparatus to a~hieve this goal consists of a housi~g in
th~ form of a large diameter tube closed on top with a lid.
Beneath this lid a stirrer i9 inserted in the center with its
diameter small er than the inner diameter of the housing. The
stirrer is attached to a rotating hollow axis~ through which
fluid is remov~d from th~ enclosed measuring volumP, circulated
by a pump and returned to the closed measuring volume through at
least one return opening in the lid or elsewhere. D~pending on
applicatio~, the bottom of the apparatus is either open (field
deployment) so that the substrate/fluid int~rface is that of the
original sediment or it is s~aled a~d the interface is that of an
i~s~rted s~diment cor2 or of a~y other desired substrate surface.
BRIEF DESCRIPTION OF THE ~WING5
The invention may be best understood by those having
ordinary skill in the art by reference to the followin~ detailed
description when considered i~ conjunction with the açcompanying
drawings in which:
~l29v7a~7
FIG. 1 is a oross-sectional elevation view of one particular
~eature of the inventio~.
FIG. 2 is a cross secti~nal elevation Yiew of a second
feature ~f the invention.
FIG. 3 is a top plan YieW of a circular housing of the
invention.
FIG. 4 is a top plan view of an elliptical housing of the
invention.
FIG. 5 is a ~ross sectional ~levati~n view of a third
feature of the invention.
FIG. 6 is a view of the device of FIG. 1 with a bottom
sealing member.
DETAILED DESCRIPTION OF THE INVENTION
The apparatus 11 of FIG. 1 consists of a circular housir.g 12
which is open at the bottom and closed by a lid 10 on top. Lid
10 is connected to housin~ 12 via a hinge 26 which permits a
hinged-type openin~ and closin~.
Beneath lid 10 a stirrer device 14 is attached which
co~sists of a circular disk 20. Disk 20 is conneeted to a hollow
stem 16 which can rDtate freely in the lid 10 y~t is sealed. The
stem 16 is dri~en by a drive wheel 28 attaohed ~utside the lid
10 .
The hollow rotating st2m 16 is ~oupled to a polyvinyl
chloride or like plastic tubing 60 which leads to a pump 24,
whose outlet side is connected to a return openin~ 18 located
~2~7~7
close to the ~enter of the lid 10.
Apparatus 11 can have a bot~om mernber 29 when used to
collect microbiological matter growing in a culture mediwn. See
FIG. 6. In the apparatus 11 or 11a the stirrer devi~e 14 or 14a
is ronnected to a stai~less Ateel tub~3 62 which in turn leads to
the tubirl~ 60. The connection of stirrer device 14 or 14a to
the steel tube 62 is made by inside 64 and outside 66 O-rings.
An acrylic ~ounter-nut 68 ~ecures disk 20 at the end of stem 16.
Slass ~al l bearings 70 separate the drive whe~l 28 ~rom the top
~eali~g blo~k 72 usually made out of T~FLON. Brace 74 prevents
st~el tube 62 from tur~ing.
Wh~n turning the hollow a~is 16 via the drive ~heel 28 by
means of a~ AC motor and variable gear box (not shown), the
stirrer device 14 is also turning. This i~ turn yenerates a
fluid flow relative to the a~is of apparatus 11. The rotation of
the stirrer device 14 produces a rotati~g flo~ of the fluid
inside the confined volum~, with the velocity ~ector decreasing
i~ ma~nitude in radial direction ~rom th~ outer diameter to~ards
the center. The stirrer devi~e 14 thus gen~rates a non
homogeneous wall shearing stress at the ~ubstr~te/fluid interface
38 which decreases accordingly in ma~nitude from larger to
smaller radii. ~hen fluid 15 is removed simultaneously through
the hollow stem 16, a further flow componsnt is gen~rated which
increases from larger to smaller radii. With appro~riate
dim~sion~ ~see Example~ below) for the tube housing 12 nd
.. ... . .. . ..
l,X~
stirrer device 14, together with a proper combination of fluid
volume recirculatet per unit time and angular velocity of the
stirrer device 14 it is possible to generate a homogeneous flow
in magnitude (but not in direction). This in turn lead~ to a
spatially homogeneous field of ~ear-bottom velocity gr~dient~ ~nd
thus to a spati~lly homoge~eous magnitude of th~ wall shearing
stress at the substrate/fluid i~terface 3~ i~side the apparatus
11 between fluid 15 and substrate 17. Other combinations of
angular velocity of stirrer device 14 ~d center-removed
recirculated fluid produce i~creasing or de~rea~ing radi~l wall
sheari~g stress distributio~s. The~e alternate combinations ar~
desirable for selected applications.
Th~ individual applications can be yrouped i~to laboratory
devices and ~ield devices, and within these groups as either flux
chambers or samplers. I~ all cases the wall shearing stress
~ields can be either spatially homogeneous or inhomogen~ous,
with their time histories then beiny steady-state, stepfunctions
~rom high to low or from low to high or varia~le. The
combinations of angular velocity of the stirrer a~d simultaneous
fluid recirculation ~an be manually selected for the simple
temp~ral st~ady-state distributio~s. For ste~ functiDns in time,
or for variable time histories su~h as cycling in general or
tidal cycle simulations specifically, or for adjustment of the
wall shearing stress field i~side a chamb~r deployed in-situ to
values measured on the outside in the u~co~fined boundary layer
... . . . .
0~74.7
digital electronics for driving pump a~d stirring device 14 are
required. Also needed is a computer program utilizing a pre-
established calibration matrix stored in a microprocessor to
select the required stirring /pumping rate combinatio~s.
In the feature show~ in FIG. 2, a skirt 22 is attached to a
shortened circular disk 20a which is aligned parallel with the
ide w~ll 40 o housing 12 but at a considerable distance from
it. It permits the introduction of probing devices 31 through
feed-through openings 30 in the lid 10 into the spac~ betwee~ the
skirt-equipped stirrer disk 20a and the housing side wall 40 such
that measurements can be taken of the fluid 15 a~d substrate 17
in the ~onf ined area . In this f~ature the invention uses the
Couette fl~w ~enerated ~etween the skirt 22 and the sidewall 40
of the housing to extend the stirrer device 14a by a liquid
addition all the ~ay to the sidewall 40, since the Couette flow
established in the ciraular gap 42 generates a constant fluid-
shearing stre~s in radial direction. This permits the boundary
layer at the substrate/fluid interface underneath this gap 42
area t~ sxperien~e the same magnitude of the wall shearing stress
a~ underneath the ~olid-material stirrin~ device 14a at smaller
radii. In this feature the stirrer device 14a i~ thus partly
solid material, partly fluid and generates the sam~ eff~ct
regardin~ the magnitude of the wall shearing stress as if a solid
disk 20 exte~ds to the sidewalls of the hou~in~ 12 as shown in
FI~. 1.
7~7
.
The shape of the disk 20 or 20a has to be selected based on
experiment~specific requirements. For example, it may be
necessary to use a disk with wedge-type radial cro~s section,
either converg~nt or divergent. Furthermore, the stirrer d~vice
14 or 14a can be foxmed by radially attached wings or blades.
Also, a perforated or a grid like disk is feasible. The stirrer
can even be shaped like a bell.
The tube housing 12 has a circul~r shape when a spatially
homogeneous wall shearing stress has to be generated at ~he
substrate/fluid interface. If a ~on-homogeneous wall shearing
stress field of known radial distribution has to be ~enerated at
th0 substrate/fluid interface instead, other cross-sectional, for
e~ample, elliptical shapes of the housing may be chosen.
Furthermore, precisely known inhomogeneous fields sf the
wall ~hearing stress increasing or decreasin~ in radial dir~ction
~an be ~enerated either by a different selection of ~he amount of
water volume removed centrally and recirculated per unit time or
by a different selection of the number of rotations of th~
stirrer per unit time compared to th combination ~etti~g of
^ctirri~g device revolutions and recircul~ted fluid volum2 per
minute for spatially homogeneous distributions.
When using the device as a laboratory simulator, it has to
b~ built in a way that it ca~ contain a substrat~ 17 of
approximately twenty cm d~pth with an overlying fluid 15 col~mn
of approximately ten cm hei~ht. Furthermore, a bottom lid 29 has
~2~)7~7
to be present which needs to be mov~ble sideways for sealing and
be removable when sediment cores are collected in the field.
For field investigations the apparatus 11b as seen in FIG. 5
has to be built such that it can be d~ployed in free-fall mode or
via cable from a vessel to land on the ocean floor. In this ca~e
no bottom lid 29 is ne~ssary t~ 3eal the apparatus 11b unles.
~ediment core~ are to be recovered after the measurement~.
The apparatu~ 11b in FIG. 5 is ~upp~rted by a superstruc~ure
45 in which i~ suspended apparatus 11b by bleeders 53. Disk 20b
i~ attached to the hollow stem 16b leading to ~ rosette sampl~r
42 with bas~ ~nd motor dr ve. The housing 12b has a sharp bottom
rim 44 to pene~rate the sea floor 17. A layer of marine snow 46
rests ~n the ~ea floor 17. Circumfsrentially attached bleeders
48 are employed for closing lid lOa whi~h h~s a reces3 50 for the
rotating disk 20b. Und~rwater housing 52 with gear bo~, drive
sha~t and motor rests on the lid 10a along with other equipment
such as underwater camera 54, pressure housing with electronics
56 and power pack SO. Vent holes or fluid replacemen~ holes 18a
are located on th~ circumference of recess 5D.
The su~erstructure 45 is lowered to the s~a floor by a cable
a~d thereafter housing 11b s~ttles usin~ ble~ders 53 until rim 44
is imbedded in the sea floor 17 to the depth of collar 55. The
bottom switch 58 u~derneath c~llar ~5 the~ a~tivates th~ clo~ing
of the lid via ble~d~rs 48. Switch 59 atta hed to lid 10a
actiYates upon closing of disk ~Ob which causes sea water
rot~tio~ in the now confined volume 15 for gen~ration of a wall
~ X 9 ~ 7 ~r~
shearing stress field. U~d~r it~ influence the marine ~now 46
accumulat2s in the center of apparatus 11b. A timed valve
activates suctio~ of fluid 15 through hollow ~tem 16b into the
rosette sampler. Additional samples are then activated through
electronicc 56 along witb the cam~ra 54. ~he super~tructure
returns to the surface for analysis of the ~amples after
completed ~ollection ~ycle.
The apparatus of this i~vention can ~e used for
investigation of either the eff2ct~ of precisely known wall
~hearing str~-~ses generated at the su~strate/fluid i~ter~ace by
o~rtain combinations of rotatio~l speed of ~he stirr~r device 14
a~d the amou~t of water removed simultaneou~ly through the center
stem 16 or 16a and reciroulated per unit time, or for sampling
the sediment particles a~d aygregates which might be eroded under
this wall shear ng stress. In the latter case, the pump
recirculation path xequires eguipment to filter out these
~edi~nt particle~ and a~gregates or to collect th0 ~luid. Such
devices filtering out sedime~t or aggregates eroded at a pre-set
bottom stress are also necessary when the task is to i~vestig3te
the remainin~ ~ediment/~orewater ~ystem.
The bottom material inside the devi~e can be an~ type of
finely grsund material ~ith porewater space or even a solid,
imp~rmeable plate either flat or with a rough sur~a~e.
8ubstrat~s for bacterial growth can also be employed.
1~
~ ~ ~ V ~ ~ 7
The fluid can be a~y chemical or chemical solution as long
as the materials of the design ensure its confinement.
Entrainment of porewater solutes, biomass and their e~udates
under selected bottom stre~s fields are also possible beyond
sediment entrainment studies with adequate filters or ~luid
samplers in the recirculation path. Thç recirculation path does
not ~eed to be closed. ~ater could be removed in controlled
volumes from the sealed housing through the hollow axis 16 and
fed to other proce~sing unit~, while the replacement fluid is
transported by another ~synchroni~ed) second pump into the
housin~ via one or several return openings. R~circulated or
replaced fluid can also provide a "spi~e" of fluid with new
characteristics, e.g. strongly reduci~g or with special chemicals
before returning to the enclosed fluid volume inside the
apparatus. Al~o, the ~ub~trate/fluid interface does not need to
be discontinuous, but can form a trong density gradient like in
fluid mud.
In FIG. 2, a ~eature is shown where the false bottom 32 of
the device is equipped with a receptacle 34 for ~ sediment core
liner 36 sealed at the ~Qttom. The diameter of the receptacle 34
is thus smaller than the radius of the false ~ottom plate 32. In
this feature it is possible to investigate reco~ered sediment
cores in a simple manner i~ a laboratory, either on land or
shipborne.
The proposed device is especially well adapted for
investigations o~ processes at th~ sedimen~/water interface of
11
~ 74 7
natural water systems. However, a wide variety of additional
applications is po~sible. For example, in microbiological
manufacturing ~rocedures it is desirable that microbiologic
populations, whose metabolic products are harvested, are ~xposed
to a controlled and precisely known flo~ velocity and thus wall
shear1ng stress. Other examples can be found in proc~ss
e~gineering, espe~ially when a well defined vertical flux of
materials has to be achieved ~etween ~ fluid ~nd a substrate.
This latter case bears relevanGe for ~urf~ce coati~gs.
For the fluid it is not necessary to be water. It even may
be air or other ~ases, carrying atomized metals, aerosols or be
other diluted two-phase systems o which one phase is se$tling on
the substrate surface in rates controlled by the wall shearing
stress.
EX~MPL~S 1-8
Particular examples of an apparatus utili~ing the inv ntion
are described below. In each of the below listed examples the
apparatus 11 has the foil~wing dimensions:
diameter of housing: 30 cm
housing height: 35 cm
sul:strats depth: 25 cm
water hei~ht from interface to lid: 10 cm
total ~onfi~ed water volume: 7 litr~
total confined ~edimerlt vol~uTe: 18 litres (depending on
insertion technigue)
12
~ 7 ~ 7
disk with skirt, diameter: 20 cm
disk with skirt, length: 4.5 cm
The following combin~tions of stirrer rotations/fluid volume
recirculation shown below generate homogeneous wall shearing
stresses (expressed by the friction velocity u* = (~ ~
where ~ = fluid de~sity) of defined magnitude over the
interfacial ar~a with errors <10% for above dimsnsions:
friction velocity u* rotation of disk fluid volume
(in cm/s) with ~kirt recirculated
(in cm /min)
(1) G.22 5 rev. in 67 sec. 95
(2) 0.30 6 rev. in 67.5 secO150
t3) 0.37 7 rev. in 60 5ec. 365
(4) 0.50 13 rev. in 58 s0c. 195
(5) 0.54 13 rev. in 60 ~ec. 424
(6) 0.69 20 rev. in 60 sec. 230
(7) 0.75 23 rev. in 60 sec. 290
(8) 1.00 ~ 30 rev. in 60 sec. 680
u* = friction velocity
= wall shearing stress
~ p = fluid density
EX~MPLES 9 - 12
E~amples producing homogeneous and inhomo~eneous wall
shearing stresses of defi~ed ma~itude over the interfacial area
f~r an apparatus with 12 cm diameter a~d 5 cm water depth:
u* (cm/s) rotation of flat disk 1uid volume
recirculat~d
~cm Imin~
13
~ ~ 9 V ~ ~7
(9) homogeneous, 0.25 10 rev. in 60 sec. 67
(10) homogeneous, 0.4 17.2 rev. in 60 sec. 90
(11) maximum at outside 17.3 rev . in 60 sec. no pumping radius: 0.45
minimum at centær:
0.13
(12) minimum at outside 17.1 rev. in 60 sec. 1000
radius: 0.3
maximum at
center 2.2
14
